Benzodeazaadenine derivative base and electronic material containing the same

ABSTRACT

A nucleic acid base for hole transportation in DNAs which does not cause oxidative decomposition; and an artificial DNA molecule which can realize effective hole transportation in DNAs while maintaining the double spiral structure of the DNAs. Provided are: a nucleic acid which contains a benzodeazaadenine derivative base represented by the general formula (I):  
                 
 
(wherein R 1 , R 2 , R 3 , R 4 , R 5 , and R 6  each independently represents hydrogen, amino, mono (lower alkyl) amino, di (lower alkyl) amino, hydroxy, lower alkoxy, halogeno, cyano, mercapto, lower alkylthio, or aryl; and R 7  and R 8  each independently represents hydrogen or a group bonded to phosphoric acid); 
and a polynucleotide comprising the nucleic acid.

TECHNICAL FIELD

The present invention relates to a nucleic acid comprising a modifiednucleic acid base that has charge transportability equal to that ofguanine and is resistant to oxidative decomposition, a polynucleotidecomprising the nucleic acid, and an electronic material comprising thepolynucleotide.

BACKGROUND OF THE INVENTION

Many researches have been made on electronic materials utilizing naturalDNAs. Conformation of higher-order structure of the natural DNAs can beeasily controlled, whereby attention has been paid to the use of thenatural DNAs as conductive molecular wires. It has been known that,although guanine (G) has the smallest oxidation potential among naturalnucleic acid bases and can effectively mediate charge transport in theDNAs, oxidative decomposition of guanine occurs as a side reaction. Onthe other hand, adenine (A) is low in charge transport efficiency thoughresistant to the oxidative decomposition. Under the above-describedcircumstances, from the viewpoint of creating a next-generationmolecular wire, development of a modified nucleic acid base, which hascharge transportability equal to that of guanine and is resistant to theoxidative decomposition, is a very interesting research theme to providea new material for the fields of nanotechnology as well as materialscience.

Thus, the present invention provides an artificial DNA, which has beenexpected to be used as a conductive nanowire.

DISCLOSURE OF THE INVENTION

The DNAs have many problems, and the main problem is deterioration dueto the oxidative decomposition of the nucleic acid bases, particularlyguanine. An object of the present invention is to solve the problem,thereby providing a nucleic acid base for hole transport in the DNAs,which does not cause the oxidative decomposition. A further object ofthe invention is to provide an artificial DNA molecule capable ofachieving effective hole transport in the DNA while maintaining thedouble helix structure of the DNA.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows results of testing an oxidative decomposition rate of anucleic acid ^(BD)A of the present invention in comparison with guanine(G) and adenine (A). In FIG. 1, the abscissa represents time (second) ofirradiation with 366 nm light, and the ordinate represents retentionratio (%) of the nucleic acids.

FIG. 2 is a photograph substituted for a drawing showing results ofevaluating charge transport in DNAs with a sequence containing a subjectbase (X) between consecutive guanine (G) sequences. In FIG. 2, thelongitudinal direction is direction of hole transport, X represents thebase between the guanines (G), and Y represents a base complementarythereto. In the transverse direction in FIG. 2, the leftmost is acontrol (con), and the cases of X-Y of ^(BD)A-cytosine (C),^(BD)A-thymine (T), guanine (G)-adenine (A), guanine (G)-cytosine (C),or adenine (A)-thymine (T) are shown at the right side thereof.

FIG. 3 schematically shows hole transport in a double-stranded DNA ofthe invention.

BEST MODE FOR CARRYING OUT THE INVENTION

As a result of synthesizing various artificial bases and examining theirantioxidant properties and hole transportabilities to solve the aboveproblem, the inventors have found that suitable for the objects is abenzodeazaadenine obtained by condensing adenine with a benzene ring atthe 7- and 8-positions to increase the charge transport efficiency dueto expansion of the conjugated system and to inhibit the addition ofwater.

Thus, the present invention relates to a nucleic acid comprising abenzodeazaadenine derivative base represented by the general formula(I):

(wherein R₁, R₂, R₃, R₄, R₅, and R₆ each independently represents ahydrogen atom, an amino group, a mono(lower alkyl)amino group, adi(lower alkyl)amino group, a hydroxyl group, a lower alkoxy group, ahalogen, a cyano group, a mercapto group, a lower alkylthio group, or anaryl group, and R₇ and R₈ each independently represents a hydrogen atomor a phosphate bond group),

-   -   or a polynucleotide comprising the nucleic acid.

Further, the invention relates to an electronic material comprising thepolynucleotide represented by the general formula (I).

The invention provides the nucleic acid comprising the benzodeazaadeninerepresented by the general formula (I) and the polynucleotide comprisingthe nucleic acid.

The polynucleotide of the invention can be produced according to thefollowing reaction formula using the nucleic acid of the invention.

wherein R₁, R₂, R₃, R₄, R₅, and R₆ are those described above, and R₇ andR₈ represent hydrogen atoms.

Thus, a reactive derivative such as the phosphoramidite derivative (9)can be produced from the nucleoside (8), and then the derivative can beefficiently converted to a DNA (10) by a DNA synthesis method such as aphosphoramidite method. A plurality of the nucleic acids of theinvention can be consecutively introduced into a DNA by such a commonDNA synthesis method, and thus-obtained DNA containing the nucleic acidof the invention can achieve efficient hole transport in the DNA.

The invention is more specifically described with reference to anexample of the nucleic acid of the invention containing a base in whichR₁ is a 2-dimethylamino-ethyleneimino group, and R₂, R₃, R₄, R₅, and R₆are hydrogen atoms.

A production example of a phosphoramidite derivative (7) of the base isshown below.

A benzodeazaadenine derivative (1) was coupled with a sugar moiety (2)to produce a compound (3), and then the chloro group at the 6-positionwas converted to an amino group to obtain a compound (4). To incorporatethe obtained compound (4) into an oligomer by the phosphoramiditemethod, protective groups were introduced into the amino group and thehydroxyl group at the 5-position, and the resultant was converted to anamidite to produce the phosphoramidite derivative (7).

The oxidative decomposition rate of thus-produced nucleoside (4) wasmeasured by HPLC using riboflavin as an oxidizing agent and comparedwith those of the other bases. The results are shown in FIG. 1. In FIG.1, the abscissa represents time (second) of irradiation with 366 nmlight, and the ordinate represents retention ratio (%) of the nucleicacids. In FIG. 1, G represents guanine, A represents adenine, and ^(BD)Arepresents a nucleic acid of the invention.

As a result, though the natural guanine (G) was rapidly decomposed asthe irradiation time proceeded, the oxidative decomposition of thenucleic acid ^(BD)A of the invention as well as adenine (A) was hardlyobserved.

Next, an oligomer containing the nucleic acid ^(BD)A of the inventionwas produced by the above-described method, and using the synthesizedoligomer, the melting temperature of a duplex was examined to evaluatethe base pairing ability of the modified nucleic acid base. As a result,it was shown that the nucleic acid ^(BD)A of the invention could form astable base pair with cytosine or thymine.

Then, the charge transportability of the modified nucleic acid base wasevaluated by performing charge transport in DNAs with a sequencecontaining a subject base between consecutive sequences of guanines (G),which are oxidatively decomposed when holes are generated in the holetransport, and cause DNA fragmentation in a subsequent alkali treatment.The results are shown in a photograph of FIG. 2 substituted for adrawing. In FIG. 2, the longitudinal direction is the direction of thehole transport, X represents the base between the guanines (G), and Yrepresents a base complementary to the base of X. In the transversedirection of FIG. 2, the leftmost is a control (con), and the cases ofX-Y of ^(BD)A-cytosine (C), ^(BD)A-thymine (T), guanine (G)-adenine (A),guanine (G)-cytosine (C), or adenine (A)-thymine (T) are shown in theright side thereof. In the assay, the samples were irradiated with 312nm light at 0° C. for 45 minutes in a sodium cacodylate buffer (10 mM,pH 7.0), and subjected to a piperidine treatment at 90° C. for 20minutes.

As a result, in the case where X was adenine (A) with a low chargetransportability, holes were not transported to the consecutive Gsequence at the 3′ side of X, and fragmentation was observed only in theconsecutive G sequence at the 5′ side. On the other hand, in the casewhere X was guanine (G) and the nucleic acid ^(BD)A of the invention,holes were transported through G or ^(BD)A, so that fragmentation wasobserved also in the consecutive G sequence at the 3′ side. As a resultof comparing the fragmentation intensities, it became clear that thenucleic acid ^(BD)A of the invention had higher charge transportabilitythan that of guanine (G). Further, the charge transport was inhibitedwhen the complementary base was changed from thymine to cytosine.

It was shown by the above results that the nucleic acid ^(BD)A of theinvention was resistant to the oxidative decomposition, had the chargetransportability equal to that of guanine, and thereby could be amodified nucleic acid base composing a DNA wire.

The electronic material of the invention comprises the DNA containingthe nucleic acid represented by the general formula (I), preferably adouble-stranded DNA. The complementary chain is preferably such that canform common Watson-Crick type base pairs. The nucleic acid of theinvention can form a stable base pair with cytosine or thymine, and thusboth cytosine and thymine can be used as a complementary base for thenucleic acid of the invention.

Although the holes are smoothly transported in the case of using thymineas the base complementary to the nucleic acid of the invention, the holetransport is inhibited in the case of using cytosine. The on/off controlof the hole transport can be achieved utilizing the above fact.

An example of the hole transport in the DNA of the invention isschematically shown in FIG. 3. FIG. 3 schematically shows hole transportin a double-stranded DNA of the invention.

In the general formula (I) according to the invention, the lower alkylgroup is preferably a straight or branched alkyl group having from 1 to15 carbon atoms, preferably 1 to 6 carbon atoms, and examples thereofinclude a methyl group, an ethyl group, etc. The lower alkoxy grouppreferably comprises a straight or branched lower alkyl group havingfrom 1 to 15 carbon atoms, preferably 1 to 6 carbon atoms, and examplesthereof include a methoxy group, an ethoxy group, etc. The aryl group isa monocyclic, polycyclic, or condensed carbocyclic group having from 6to 30 carbon atoms, preferably 6 to 14 carbon atoms, or a monocyclic,polycyclic, or condensed, 5- to 7-membered, heterocyclic group having atleast 1 to 3 nitrogen, oxygen, or sulfur atoms in the ring, and specificexamples thereof include a phenyl group, a naphtyl group, a furyl group,a thienyl group, etc. These aryl groups may have a substituent such as alower alkyl group, a lower alkoxy group, and an amino group.

In the general formula (I), the phosphate bond group includes aphosphate group such as a phosphoramidite group, or a phosphate group toform a DNA.

The nucleic acid of the invention, represented by the general formula(I), shows the charge transportability equal to that of guanine and thelow oxidative decomposition rate equal to that of adenine, so that theDNA containing the nucleic acid of the invention is remarkably useful asa conductive nanowire. The DNA of the invention obtained by introducingthe artificial nucleic acid base into DNA, which mediates the holetransport in the DNA, is remarkably useful as a next-generationmolecular wire usable for (1) DNA nanowires, (2) fluorescent nucleicacid bases, (3) antisense or antigene DNAs for controlling geneexpression including DNA replication, RNA transcript, proteinrecognition, etc., (4) labeled DNAs for hybridization, intended to beused in desired base sequence recognition or single nucleotidepolymorphism scan, and (5) molecular logic circuits, biosensors, etc.

EXAMPLES

The present invention will be described in more detail below withreference to Examples without intention of restricting the scope of theinvention.

Example 1 Production of4-chloro-9-(2′-deoxy-β-D-erythro-pentofuranosyl)-9H-pyrimido[4,5-b]indole(Compound 3)

4-chloro-1H-pyrimido[4,5-b]indole (1) (360 mg, 1.77 mmol) was suspendedin dry acetonitrile (250 mL) at room temperature. To the suspension wasadded sodium hydride (60% in oil; 142 mg, 3.54 mmol), and the mixturewas refluxed under stirring for 10 minutes. Then, ribose (2) (687 mg,1.77 mmol) was added thereto and stirred at room temperature for 1 hour.The reaction mixture was concentrated and purified by a columnchromatography (silica gel, a hexane solution containing 20% ethylacetate) to obtain the compound (3) (890 mg, 91% yield).

¹H NMR (CDCl₃) δ; 38.71 (s, 1H), 8.36 (d, 1H, J=7.9 Hz), 7.99 (d, 2H,J=8.2 Hz), 7.95 (d, 2H, J=6.6 Hz), 7.79 (d, 1H, J=8.4 Hz), 7.37 (dt, 1H,J=8.1, 0.7 Hz), 7.28 (d, 2H, J=8.1 Hz), 7.27 (dt, 1H, J=8.2, 1.1 Hz),7.23 (d, 2H, J=8.4 Hz), 7.03 (dd, 1H, J=8.8, 6.2 Hz), 5.93 (dt, 1H,J=6.2, 2.7 Hz), 4.86 (dd, 2H, J=11.1, 3.5 Hz), 4.59 (dd, 1H, J=7.2, 3.9Hz), 3.56 (ddd, 1H, J=16.1, 7.5, 7.2 Hz), 2.59 (ddd, 1H, J=14.4, 6.2,2.4 Hz), 2.43 (s, 3H), 2.41 (s, 3H);

¹³C NMR (CDCl₃) δ; 166.2, 166.1, 155.6, 153.5, 152.7, 144.4, 144.0,137.8, 129.8, 129.7, 129.3 129.2, 128.3, 126.9, 126.5, 123.4, 122.6,119.1, 112.8, 112.1, 83.6, 81.8, 74.4, 63.8, 35.3, 21.73, 21.70;

MS (FAB, NBA/CH₂Cl₂) m/z (%) 556 [(M+H)⁺] HRMS (FAB) Calculated valuefor C₃₁H₂₇ClN₃O₇ 556.1639, [(M + H)⁺] Observed value 556.1638.

Example 2 Production of4-amino-9-(2′-deoxy-β-D-erythro-pentofuranosyl)-9H-pyrimido[4,5-b]indole(Compound 4)

The compound 3 obtained in Example 1 (300 mg, 0.54 mmol) was suspendedin 20 mL of methanolic ammonia (saturated at −76° C.), and stirred at150° C. for 10 hours in a closed vessel. Then, the solution in thevessel was concentrated and purified by a column chromatography (silicagel, a chloroform solution containing 5% methanol) to obtain thecompound (4) (117 mg, 72% yield).

¹H NMR (DMSO-d₆) δ; 38.31 (d, 1H, J=7.7 Hz), 8.27 (s, 1H),7.84(d, 1H,J=8.2 Hz), 7.37 (dt, 1H, J=8.2, 1.1 Hz), 7.32-7.25 (3H), 6.82 (dd, 1H,J=8.8, 6.0 Hz), 5.32 (d, 1H, J=4.4 Hz), 5.28 (t, 1H, J=4.9 Hz), 4.46 (m,1H), 3.86 (dd, 1H, J=7.3, 3.8 Hz), 3.66 (m, 2H), 2.88 (ddd, 1H, J=15.6,8.8, 6.6 Hz), 2.05 (ddd, 1H, J=15.4, 6.0, 2.2 Hz);

¹³C NMR (DMSO-d₆) δ; 157.7, 154.7, 154.4, 135.5, 124.7, 121.3, 121.0,120.2, 111.8, 87.1, 82.8, 70.9, 61.9, 37.5, 31.5;

MS (FAB, NBA/CH₂Cl₂) m/z (%) 301 [(M+H)⁺] HRMS (FAB) Calculated valuefor C₁₅H₁₇N₄O₃ [(M + H)⁺] 301.1301 Observed value 301.1297

Example 3 Production of(4-N,N′-dimethylaminomethylidene)amino-9-(2′-deoxy-β-D-erythro-pentofuranosyl)-9H-pyrimido[4,5-b]indole(Compound 5)

N,N-dimethylformamide (5 mL) solution of the compound 4 obtained inExample 2 (130 mg, 0.43 mmol) and N,N-dimethylformamide dimethylacetal(5 mL, 28.3 mmol) was stirred at 55° C. for 18 hours. The reactionmixture was concentrated to obtain a brown oily matter. The oily matterwas purified by a column chromatography (silica gel, a chloroformsolution containing 10% methanol) to obtain the compound (5) (134 mg,87% yield).

¹H NMR (CDCl₃) δ; 38.94 (s, 1H), 8.53 (s, 1H), 8.41 (d, 1H, J=7.1 Hz),7.49 (d, 1H, J=8.1 Hz), 7.44 (dt, 1H, J=7.1, 1.1 Hz), 7.30 (dt, 1H,J=7.8, 0.9 Hz), 6.73 (dd, 1H, J=8.9, 5.5 Hz), 4.83 (d, 1H, J=5.1 Hz),4.23 (s, 1H), 4.01 (dd, 1H, J=2.9, 1.4 Hz), 3.82 (m, 1H), 3.31 (s, 3H),3.29-3.22 (m, 2H), 3.21 (s, 3H), 2.225 (dd, 2H, J=15.4, 5.7 Hz);

¹³C NMR (CDCl₃) δ; 161.9, 156.8, 155.2, 153.1, 137.9, 125.9, 123.7,121.4, 121.0, 108.9, 88.8, 85.7, 74.0, 63.8, 41.2, 39.9, 35.2, 31.4;

MS (FAB, NBA/CH₂Cl₂) m/z (%) 356 [(M+H)⁺] HRMS (FAB) Calculated valuefor C₁₈H₂₂N₅O₃ [(M + H)⁺] 356.1723 Observed value 356.1722

Example 4 Production of(4-N,N′-dimethylaminomethylidene)amino-9-(2′-deoxy-5′-O-dimethoxytrityl-β-D-erythro-pentofuranosyl)-9H-pyrimido[4,5-b]indole(Compound 6)

The compound 5 obtained in Example 3 (130 mg, 0.37 mmol),4,4′-dimethoxytrityl chloride (16.1 mg, 0.48 mmol), and4-dimethylaminopyridine (13 mg, 0.11 mmol) were added to anhydrouspyridine (10 mL), and stirred at room temperature for 2 hours. Thereaction mixture was concentrated to obtain a brown oily matter. Theoily matter was purified by a column chromatography (silica gel, a mixedsolution of 50:50:5 (v/v/v) of hexane, ethyl acetate, and triethylamine)to obtain the compound (6) (66 mg, 33% yield).

¹H NMR (CDCl₃) δ; 38.91 (s, 1H), 8.53 (s, 1H), 8.39 (d, 1H, J=7.7 Hz),7.70 (d, 1H, J=8.3 Hz), 7.43 (dd, 2H, J=8.6, 1.5 Hz), 7.31 (dd, 4H,J=9.0, 1.5 Hz), 7.27-7.13 (5H), 6.94 (t, 1H, J=7.3 Hz), 6.75 (dt, 4H,J=9.9, 3.1 Hz), 4.85 (dt, 1H, J=7.7, 4.4 Hz), 4.04 (q, 1H, J=4.6 Hz),3.747 (s, 3H), 3.745 (s, 3H), 3.48 (d, 1H, J=4.6 Hz), 3.30 (s, 3H), 3.21(s, 3H), 3.25-3.19 (m, 1H), 2.29 (ddd, 1H, J=13.7, 7.0, 3.8 Hz);

¹³C NMR (CDCl₃) δ; 161.3, 158.4, 156.52, 156.47, 154.0, 144.7, 136.8,135.8, 130.14, 130.11, 128.2, 127.8, 126.8, 125.6, 123.5, 121.8, 121.4,113.1, 111.7, 105.6, 86.5, 84.5, 82.7, 72.6, 63.6, 60.4, 55.2, 45.6,41.0, 37.7, 35.1, 21.1, 14.2;

MS (FAB, NBA/CH₂Cl₂) m/z (%) 658 [(M+H)⁺] HRMS (FAB) Calculated valuefor C₃₉H₄₀N₅O₅ [(M + H)⁺] 658.2951 Observed value 658.3038

Example 5 Production of(4-N,N′-dimethylaminomethylidene)amino-9-(2′-deoxy-5′-O-dimethoxytrityl-β-D-erythro-pentofuranosyl-3′-O-cyanoethyl-N,N′-diisopropylphosphoramidate)-9H-pyrimido[4,5-b]indole(Compound 7)

The compound 6 obtained in Example 4 (10 mg, 15.2 mmol),N,N,N′,N′-tetraisopropyl-2-cyanoethyl-diphosphoramidate (5.3 μL, 16.7mmol), and tetrazole (1.2 mg, 16.7 mmol) were added to acetonitrile (400μL), and stirred at room temperature for 2 hours. The obtained matterwas separated by filtration and used for the next step without furtherpurification.

Example 6 Production of Oligonucleotide

A desired oligonucleotide was produced by a common phosphoramidatemethod using a nucleotide synthesizer (302 DNA/RNA (AppliedBiosystems)). The obtained oligonucleotide was purified by reverse phaseHPLC (5-ODS-H column (10×150 mm, 0.1 M triethylamine acetate salt waseluted with the linear gradient of 5-20% acetonitrile for 30 minutes atpH 7.0 at the flow rate of 3.0 mL/minute)). To identify the producedoligonucleotide, an oligonucleotide containing 2-amino-7-deaza-dA wascompletely digested at 37° C. for 3 hours using calf intestinal alkalinephosphatase (50 U/mL), snake venom phosphodiesterase (0.15 U/mL), and P1nuclease (50 U/mL). The digested solution was analyzed by HPLC (COSMOSIL5C-18AR or Chemcobond 5-ODS-H column (4.6×150 mm, 0.1 M triethylamineacetate salt was eluted with the linear gradient of 0-10% acetonitrilefor 20 minutes at pH 7.0 at the flow rate of 1.0 mL/minute)). Theconcentration of each oligonucleotide was determined by comparing withpeaks of a standard solution containing 0.1 mM of dA, dC, dG, and dT.

Example 7 Measurement of Melting Temperature (Tm)

The melting temperature (Tm) of the double-stranded oligonucleotide wasmeasured in a buffer containing 10 mM sodium cacodylate (pH 7.0). Thecorrelation between absorption and temperature was measured at 260 nmusing JASCO TPU-550 spectrometer equipped with JASCO TPU-436 temperaturecontrol unit. The absorption of the sample was monitored at 260 nm at 2to 80° C. (temperature rise rate of 1° C./minute). The Tm value wascalculated from the result of the measurement.

Example 8 Preparation of 5′-³²P-end-labeled Primer

A primer for a polymerase elongation reaction (400 pmol of strandconcentration) was labeled by a common method of phosphorylation using 4μL of [γ-³²P]ATP and 4 μL of T₄ polynucleotide kinase. The labeled5′-end oligonucleotide was collected by ethanol precipitation. Theoligonucleotide was purified by 15% non-denaturing gel electrophoresisand isolated by a crash and soak method.

Example 9 Decomposition of 5′-³²P-end-labeled oligonucleotide by LightIrradiation in the Presence of Cyanobenzophenones Connected byoligo-deoxynucleotide

A sample solution was prepared by hybridization using a mixture ofcooled radioactive-labeled double-stranded oligonucleotides (1 μM) in asodium phosphate buffer (pH 7.0). The hybridization was achieved byheating the sample to 90° C. for 5 minutes, and then by slowly coolingto room temperature. The double-stranded 5′-³²P-end-labeled ODN(oligonucleotide) was irradiated with 312 nm light at 0° C. for 60minutes. After the irradiation, 10 μL of herring sperm DNA, 10 μL of 3 Msodium acetate, and 800 μL of ethanol were added to precipitate all thereaction products. The precipitated DNA was washed with 100 μL of 80%cold ethanol and dried under reduced pressure. The precipitated DNA wasdissolved in 50 μL of 10% piperidine, heated at 90° C. for 20 minutes,and concentrated. The radioactivity of the sample was measured by ALOKA1000 liquid scintillation counter, and the dried DNA pellet wassuspended in 80% formamide loading buffer (80% formamide solution of 1mM EDTA, 0.1% xylenecyanol, and 0.1% Bromophenol Blue). The reactionsaccording to Gilbert-Maxim G+A sequencing reaction were carried out byheating at 90° C. for 3 minutes and by rapidly cooling with ice. Thesample (1-2 μL, 2-5×10³ cpm) was placed in a gel of 15% polyacrylamide/7M urea, electrophoresed at 1900 V for 60 minutes, transferred to acassette using FUJI X-ray film RX-U, and stored at −80° C. The gel wasanalyzed by an automatic radiography equipped with a tension meter andby BIO-RAD molecular analysis software (Ver. 2.1). The intensity of thespots obtained by the piperidine treatment was determined by a volumeintegrator.

Industrial Applicability

The present invention provides the novel artificial nucleic acid basecapable of being incorporated into DNAs to form nanowires, in whichholes can be freely transported in the DNAs. The nucleic acid base ofthe invention is more resist to decomposition due to water or oxygenmolecules as compared with the natural DNA bases. Further, thefluorescence emission intensity of the base of the invention is changeddepending on a base in the complementary chain, so that the base of theinvention can be applied for reading base sequence. Furthermore, thenucleic acid base of the invention can form a base pair with a pluralityof types of natural bases, and the hole conduction rate is changeddepending on the complementary base forming the base pair, whereby thebase of the invention can be used for determining the type of thecomplementary base forming the base pair or for controlling the holeconduction rate.

1. A nucleic acid represented by the general formula (I):

(wherein R₁, R₂, R₃, R₄, R₅, and R₆ each independently represents ahydrogen atom, an amino group, a mono(lower alkyl)amino group, adi(lower alkyl)amino group, a hydroxyl group, a lower alkoxy group, ahalogen, a cyano group, a mercapto group, a lower alkylthio group, or anaryl group, and R₇ and R₈ each independently represents a hydrogen atomor a phosphate bond group), or a polynucleotide comprising the nucleicacid.
 2. The nucleic acid according to claim 1, wherein R₁ is an aminogroup, and R₂, R₃, R₄, R₅, R₆, R₇, and R₈ are hydrogen atoms in thegeneral formula (I).
 3. The polynucleotide according to claim 1, whereinthe polynucleotide is an oligomer of the nucleic acid represented by thegeneral formula (I).
 4. An electronic material comprising thepolynucleotide according to claim
 1. 5. The polynucleotide according toclaim 2, wherein the polynucleotide is an oligomer of the nucleic acidrepresented by the general formula (I).
 6. An electronic materialcomprising the polynucleotide according to claim
 2. 7. An electronicmaterial comprising the polynucleotide according to claim 3.